Java 8 Stream 将元素添加到列表和求和中

问题描述

我相信接下来我可以在 listOfPricedObjects 上使用一个流操作:

I believe I can do next using one stream operation on listOfPricedObjects:

List<BigDecimal> myList = new ArrayList();
myList = listOfPricedObjects.stream().map(PricedObject::getPrice).collect(Collectors.toList());
BigDecimal sum = listOfPricedObjects.stream().map(PricedObject::getPrice).reduce(BigDecimal.ZERO, BigDecimal::add)

如何在 myList 中填写价格并使用流一次计算价格总和?谢谢

How I can fill myList with prices and calculate sum of prices using stream one time? Thanks

UPD:结果我需要用价格填充 myList 并用 sum 变量求和.但不是使用 stream() 两次.

UPD: As the result I need myList filled with prices and sum variable with sum. But not with usding stream() twice for that.

推荐答案

您可以使用 peek 并在应用缩减的同时添加到新的 list

You can use peek and add to a new list while applying the reduction

List<BigDecimal> newList = new ArrayList<>();
BigDecimal sum = list.stream()
                     .map(PricedObject::getPrice)
                     .peek(newList::add)
                     .reduce(BigDecimal.ZERO, BigDecimal::add);

如果您有兴趣将 parallelStream 与非并发集合一起使用，请查看 Tunaki 的答案，这是有意义的，因为 sum 是一个令人尴尬的并行任务.

Please look at Tunaki answer if you interested in using a parallelStream with a non concurrent collection which makes sense since sum is an embarrassingly parallel task.

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